The current study is being conducted to determine whether administering Adriamycin and Cyclophosphamide with or without tamoxifen for four cycles is more effective than administering cyclophosphamide, methotrexate, and 5-fluorouracil for six cycles with or without tamoxifen. Women with node- negative breast cancer and pathological tumor size > 1.0 cm who have undergone lumpectomy or total mastectomy and axillary dissection and whose tumor estrogen receptors have been assayed and found to be < 10 fmol/mg cytosol protein by either the dextran-coated charcoal or sucrose- density gradient methods, or < 15 fmol/mg by the enzyme immunoassay method will be eligible. If the immunocytochemical assay (ER-ICA) is used and is reported as negative, it will also be acceptable. Some form of progesterone-receptor analysis must be perfomred and the results submitted. Progesterone analysis may include quantitative or qualitative (PR-ICA) methods. Patients will be stratified by age, clinical tumor size, and type of operation.